The present invention relates to flowmeters of the type that sense the flow of process fluid in industrial process plants. More specifically, the present invention relates to measurement of flow using a magnetic flowmeter.
Magnetic flowmeters are known in the art and typically utilize an electrically insulated flow tube that carries a flow of process fluid past an electromagnetic coil and past a pair of electrodes. The electromagnetic coil applies an electromagnetic field to the flowing process fluid. Due to Faraday's Law of electromagnetic induction, a voltage or Electromotive Force (EMF) is generated between the pair of electrodes in the fluid. This voltage is a function of the strength of the applied magnetic field and is proportional to the fluid's rate of flow.
The magnetic field can be generated by moving electrical charges. The magnetic field is often described using a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by a vector which has a direction and a magnitude (strength). The direction of the vector is determined by the direction in which the current is flowing through the coil. The strength and density of the magnetic field depends on the amount of the current and the area and shape of the coil. In particular, the total strength of the magnetic field increases with the length of the wire. For example, when a wire carrying a current is formed into a loop, the magnetic field concentrates inside the loop. When the wire is bent into multiple loops to form the coil, the magnetic field becomes even more concentrated.